This invention relates to metal fasteners for use in the construction trade and especially to fasteners known as strut nuts that are used for fastening channels, brackets, upright supports and cross members in steel structures. More particularly the invention relates to a method for making strut nuts by which serrations for gripping a structural base are formed and the metal is worked to a desired hardness.
Strut nuts are constructed primarily for a specific use but are capable of some limited general uses as well. The specific use for which the nut is intended, is for securing fittings or other items to a structural product known in the trade as "UNISTRUT". This is a rectangular metal channel in which the edge portions of the "legs" or flanges of the channel are turned inwardly 180.degree.. Thus the UNISTRUT has a rectangular cross section with one face having a slot of smaller width than the face itself and with a pair of inwardly projecting flanges defining the slot. The inwardly facing edges of the flanges are double beveled to present a sharp edge.
In the strut nut fastening assembly to which the invention relates a nut with biting portions formed in one face and generally a helical spring or the like in engagement with the opposite face, is slid along the UNISTRUT member to a desired location with the biting portions of the nut in engagement with the sharp edges of the UNISTRUT flanges. The helical spring urges the nut against the edges of the flanges to firmly locate the nut in its selected position. A threaded fastener may then be threaded into the nut to anchor other structure to the UNISTRUT member. Such nuts and the assembly thereof are shown in U.S. Pat. Nos. 3,049,161 and 3,050,355.
In the past strut nuts have been produced by (1) forming a tapped hole in a nut blank formed of mild steel, (2) cutting serrations or other biting portions in the one face and then (3) heat treating the resulting product to harden the serrations or other biting portions. This procedure requires expensive tooling and a costly heat treating step.
The method of the present invention avoids certain of the disadvantages indicated above and affords other features and advantages heretofore not obtainable.